1. Field of the Invention
The present invention relates generally to a timing error detector and a method thereof, and more particularly, to a timing error detector for a baseband transmission system using a Tomlinson-Harashima precoder.
2. The Prior Arts
In a transmission channel of a high speed digital transmission system, there are many unavoidable noise sources, which provide noises interfering clock signals recovered by the receiver side. Such noise interferences may cause large jitters, and therefore the receiver side cannot recover information transmitted from the transmitter side. As such, correct timing error information is very important for a high speed digital transmission system, such as a 10 GBASE-T baseband transmission system. Accordingly, an effective technology of extracting the timing error information is very much desired by a receiver, for overcoming the problem caused by the noise contained in the correct timing error information, thus obtaining the correct timing error information as desired.
Nowadays, data transmission rates are developed to be higher and higher. As such, the system unit interval becomes much shorter. When the system is in operation with a higher data transmission rate, the timing margins of the system are closer to each other. Therefore, the performance of a timing recovery (TR) loop plays a critical role hereby. Typically, a decision feedback equalizer (DFE) includes two parts, a feedforward equalizer (FFE), and a feedback equalizer (FBE). To solve the error propagation problem, a Tomlinson-Harashima precoder (THP), which is known as a transmitter side pre-equalization technique, has been proposed to move the FBE of the DFE to the transmitter side. The THP is not only capable of avoiding the error propagation problem, but also compatible with the low density parity check (LDPC) codes, thus reducing the impact to the system and lowering the operation risk of the system.
One of the most important blocks in a TR loop is the timing error detector (TED), such as a Mueller and Muller TED (MM-TED) or an equalizer-based TED (EQ-TED). The MM-TED has been widely used in many TR systems. In a typical MM-TED, the output of the TED is determined according to the sampled data and estimated data values. The EQ-TED estimates the timing error information according to the coefficients of the FFE. The EQ-TED does not need any decision results for estimating the timing error, and therefore it can be applied in a receiver for a baseband transmitter using THP.
The present invention is provided as a solution to problems of the conventional MM-TED. In a THP of a baseband transmitter, the THP employs a modular element for restricting the output within a predetermined range, which causes a non-linear effect, and therefore the MM-TED of the baseband communication system using the DFE cannot detect the correct timing error information. Moreover, the conventional EQ-TED has the following disadvantages. Firstly, an optimal first precursor tap weight obtained at an optimal sampling phase is assumed to be known, in that only when an optimal coefficient of the FFE is known, the system can obtain the correct timing error information. Otherwise, the EQ-TED would be biased. Secondly, the estimated timing error is related to the algorithm for dynamically adjusting the FFE coefficient, and accordingly different estimated values of the timing error may be obtained in accordance with different adaptive algorithms.
As such, a timing error detector and a method thereof are desired to provide a solution to the problems associated with the conventional technologies, and thus improving the performance of the entire communication system.